Effects of Surface Drainage on Sediment Yield in Southern Delaware

Sediment surveys were conducted over a period of 16 years on two small reservoirs in the Nanticoke River basin, Delware in order to assess the effects of watershed drainage projects on sediment yield. Herns Pond was used as a control watershed in which no drainage improvement activities were performed while Fleetwood Pond lies at the downstream end of Tyndall Branch in which 38.2 miles of channel were improved to provide drainage. Land use did not change significantly in the Fleetwood Pond watershed after drainage was improved. After 16 years, Herns Pond is accumulating sediment at the annual rate of .110 tons per acre of contributing area as compared to .053 tons per acre in Fleetwood Pond. The lower yield in Fleetwood Pond appears to be due to: an increase in infiltration and decrease in surface runoff; more crop cover and residue on farmland; ability to use conservation tillage methods on drained cropland; and use of in-channel sediment traps during and after construction.